Mineralogical Characterization of the Early Silurian Shales as Encountered in Southern Tunisia

This study presents whole rock and clay fraction analysis of the Silurian Argiles Principales Formation from southern Tunisia Berkine Basin. The organic-rich Hot Shale interval is marked by prevalent illite amount compared with the overlying succession. However, enhanced preservation of widespread enrichment of kaolinite that marks the overlying shales with small variability of chlorite and I/S is being noted. The predominance of the kaolinite on top of the ?Hot shale? Member is interpreted as being derived chiefly from acid conditions capable of generating processes of preservation resulting from intense feldspars decomposition under strong acid water drainage. The elevated organic matter preservation is probably inferred from increased primary productivity and redox conditions testified by the presence of small-sized pyrite framboids and probable microbial mats at the bottom water interface during subsequent burial of the Silurian sediments. This may indicate shallow and calm anaerobic environment resulting from activity of sulfate-reducing bacteria during the early Silurian. This has been tied to an echo of intensified oxygen minimum zone expansion along the Gondwana margins during global to regional anoxic mass?extinction events (Sandvika, Ireviken, Mulde and Lau). In this paper, we present new nomenclature related to the studied Silurian shales in southern Tunisia.